U.S. patent number 4,324,110 [Application Number 06/199,130] was granted by the patent office on 1982-04-13 for spiral-type heat exchanger.
This patent grant is currently assigned to Air Products and Chemicals, Inc.. Invention is credited to Norris G. Lovette, Jr., David R. Ruprecht.
United States Patent |
4,324,110 |
Lovette, Jr. , et
al. |
April 13, 1982 |
Spiral-type heat exchanger
Abstract
A system for heating or cooling articles conveyed in a vertical
helical path is defined by an endless conveyor belt driven at its
inner edge by contact with a rotating drum and a circulating heat
exchange fluid propelled horizontally onto the articles by axial
flow fans rotating in a vertical plane. The system features a novel
arrangement employing scroll means for confining the circulating
heat exchange fluid to a substantial portion of the helical path
and location of fan means such that the heat exchange fluid is
propelled in push-pull manner from the discharge side of one fan
means to the intake or suction side of a second fan means. In the
preferred embodiment directed to refrigeration of conveyed
articles, more particularly foodstuffs to be frozen, the conveyor
is located within an insulating housing. Further featured novelty
includes location of the driving means for the rotating drum
externally of the housing and directing of refrigerant, such as
liquid CO.sub.2 into the fan blast in a direction counter to that
of the blast.
Inventors: |
Lovette, Jr.; Norris G.
(Breinigsville, PA), Ruprecht; David R. (Laurys Station,
PA) |
Assignee: |
Air Products and Chemicals,
Inc. (Allentown, PA)
|
Family
ID: |
22736346 |
Appl.
No.: |
06/199,130 |
Filed: |
October 22, 1980 |
Current U.S.
Class: |
62/381;
62/63 |
Current CPC
Class: |
F25D
3/11 (20130101); B65G 21/18 (20130101); F25D
25/04 (20130101); B65G 2207/24 (20130101); F25D
2400/30 (20130101) |
Current International
Class: |
F25D
25/04 (20060101); F25D 3/10 (20060101); F25D
25/00 (20060101); F25D 3/11 (20060101); B65G
21/18 (20060101); B65G 21/00 (20060101); F25D
025/02 () |
Field of
Search: |
;62/63,381 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"Ashworth Lotension Spiralcage System" described in Ashworth
Bulletin No. 071 (1970) pp. 10-11..
|
Primary Examiner: Capossela; Ronald C.
Attorney, Agent or Firm: Dannells, Jr.; Richard A. Innis; E.
Eugene Simmons; James C.
Claims
What is claimed:
1. In a heat exchanger comprising an insulating housing having an
inlet and an outlet, a horizontally rotating drum positioned in a
supporting framework within said housing, conveyor means in the
form of a continuous flat belt winding around the circumferential
wall of said drum and defining a vertical helical path between said
inlet and said outlet for passage of product through said housing,
means for changing the temperature of circulating heat exchange
fluid within said housing, wherein said drum is rotatively driven
by a central drive shaft within said drum; the improvement which
comprises a supporting superstructural framework positioned
externally over the roof of said insulating housing; bearing means
mounted in said superstructure; the drive shaft for said drum
extending through the roof of said housing and being journaled in
said bearing; mechanical means connected go the shaft extension
outside said housing for rotating said shaft; said supporting
framework within said housing has mounted therein at at least two
diagonally opposed positions thereof a bank of axial flow fans
blowing inwardly along said helical path of travel of said conveyor
belt, each such bank comprising at least two fans; said means for
changing the temperature of said circulating heat exchange fluid
comprises a fluid discharge nozzle positioned adjacent each fan for
discharging liquid refrigerant into the fan blast in a direction
counter to that of the blast to effect rapid vaporization of said
refrigerant; scroll means provided at each bank of fans to confine
the path of heat exchange fluid movement propelled by said fans,
said scroll means extending continuously from a position adjacent
the periphery of the helix formed by said belt around the rotating
drum and extending at least part of the way along the outer
periphery of said belt, thereby causing said heat exchange fluid to
flow along the path of said belt for a substantial part of its flow
distance from the discharge side of one bank of fans to the intake
of a second bank of fans where the negative pressure of said second
bank exits.
2. The improvement as defined in claim 1 wherein said bearing means
mounted in said superstructure framework is a radial-thrust bearing
from which the drive shaft is suspended.
3. In a heat exchanger comprising an insulating housing having an
inlet and an outlet, a horizontally rotating drum positioned in a
supporting framework within said housing, conveyor means in the
form of a continuous flat belt winding around the circumferential
wall of said drum and defining a vertical helical path between said
inlet and said outlet for passage of product through said housing,
means for changing the temperature of circulating heat exchange
fluid within said housing, wherein said drum is rotatively driven
by a central drive shaft within said drum; the improvement which
comprises having mounted in said supporting framework within said
housing at at least two diagonally opposed positions thereof a bank
of axial flow fans blowing inwardly along said helical path of
travel of said conveyor belt, each such bank comprising at least
two fans; said means for changing the temperature of said
circulating heat exchange fluid comprises a fluid discharge nozzle
positioned adjacent each fan for discharging liquid refrigerant
into the fan blast in a direction counter to that of the blast to
effect rapid vaporization of said refrigerant; scroll means
provided at each bank of fans to confine the path of heat exchange
fluid movement propelled by said fans, said scroll means extending
continuously from a position adjacent the periphery of the helix
formed by said belt around the rotating drum and extending at least
part of the way along the outer periphery of said belt, thereby
causing said heat exchange fluid to flow along the path of said
belt for a substantial part of its flow distance from the discharge
side of one bank of fans to the intake of a second bank of fans
where the negative pressure of said second bank exits.
Description
The present invention relates to systems for heating or cooling
articles while being conveyed through a heat exchange enclosure. It
is particularly concerned with such systems employing a conveyor
for such articles traversing a spiral path within such
enclosure.
BACKGROUND OF THE INVENTION
Spiral conveyor systems employing an endless belt conveyor
travelling around the periphery of a vertically mounted cage or
drum have been commercially employed for heating or cooling various
products. Such a system for fast freezing of food products, for
example, is disclosed in U.S. Pat. No. 3,733,848, wherein the
products are passed in a vertical helical path within an insulated
housing and are contacted with cold CO.sub.2 gas blown generally
tangentially across the conveyor flights.
Among the known spiral conveyor types that have been employed in
such heating and/or cooling systems are those disclosed in U.S.
Pat. No. 3,348,659 and other patents assigned to Ashworth Bros.,
Inc. One such commercial system widely known in the industry is the
"Ashworth Lotension Spiralcage System", described in Ashworth
Bulletin No. 071 (1970).
SUMMARY OF THE INVENTION
Among the objects of the present invention is to provide a novel
heat exchanger system affording greater thermal efficiency for
heating or cooling articles traversing an essentially helical
vertical path. This is accomplished, in accordance with the
invention, by utilization of fans arranged in a push-pull manner
for propelling of heating or cooling fluid across the product being
treated and the provision of a scroll case design to reduce the
cross-sectional area of the gas flow path, thereby decreasing the
volume of gas which need be circulated to achieve the desired
velocity across the product and thereby conserving the velocity
energy of the gas stream.
In accordance with a preferred embodiment of the invention, but not
restricted thereto, the novel system is utilized for refrigeration,
particularly in rapid freezing of food products carried on the
conveyor traversing a vertical helical path, wherein a cold gas is
blown across the conveyed products by fans and the temperature of
circulating heat exchanger fluid is regulated by injection of
liquid CO.sub.2 or liquid nitrogen into the path of the moving gas
stream. In the case of using CO.sub.2 as the refrigerant, the
system of the invention is effective in reducing or eliminating
solid CO.sub.2 build-up otherwise normally present at the lower,
more desirable operating temperatures. Thus, the transfer of heat
from the recirculating gas to the potentially solid CO.sub.2 is
improved by confining the circulating gas to an essentially well
defined circuit allowing the liquid CO.sub.2 refrigerant to be
injected at the proper gas temperature point in this circuit, where
the gas/solid temperature difference is high enough to completely
sublime the nucleate snow. In the case of other refrigerants, such
as liquid nitrogen for example, the arrangement of the fans and the
essentially confined path obtained by the scroll arrangement lead
to more efficient vaporization of the injected liquid
refrigerant.
Further control over CO.sub.2 snow sublimation or rapid
vaporization of other injected liquid refrigerant is achieved by
locating the points of injection directly in the recirculating gas
stream; the points of injection being positioned such that the
direction of the jet of refrigerant is against the direction of the
circulating gas stream. In the case of liquid CO.sub.2 injection
such arrangement strips the nucleate snow particles of the
accompanying cold-gas envelope, exposing them to the warmer
circulating gas stream before they coalesce into larger particles
with lower surface to volume ratios.
The system in accordance with the invention utilizes at least two
axial flow fan means rotating in substantially vertical planes for
circulating heat exchange fluid in a substantially horizontal flow
path across the product being moved in a vertical helical path by
an endless belt conveyor. Scroll means are provided along the outer
periphery of the conveyor to define the path of the heat exchange
fluid substantially coincident with the helical path of the
conveyor, and the several fans are so arranged with respect to one
another such that the propulsion of one of said fan means drives
the circulating heat exchange fluid along the conveyor path to a
position where the negative pressure of the intake of a companion
fan exists.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partially schematic plan view taken along the line 1--1
of FIG. 2, with a portion broken away.
FIG. 2 is a vertical elevation, partly in section taken along line
2--2 of FIG. 1.
FIG. 3 is a partial horizontal section taken along line 3--3 of
FIG. 1.
FIG. 4 is an enlarged partial vertical section showing the driving
means for the drum or cage.
DESCRIPTION OF PREFERRED EMBODIMENT
Referring now to FIGS. 1 and 2 of the drawings, there is depicted a
supporting structure 10 comprising a plurality of spaced uprights
11 rigidly affixed to bottom member 12 and supplementary supports
13. Superimposed on the supporting structure 10, by rigid
attachment thereto or integral therewith is a superstructural
framework 15. A rotatable cage or drum 16 is located within the
supporting structure, said cage or drum serving as driving means
for a multiple tier belt conveyor 17, the inner edges of which are
in sliding frictional engagement with the periphery of the drum to
form a vertical helix around the drum (FIG. 4) providing a
continuous conveyor passage between its lower flight level and its
upper flight level, in the selected direction of movement of the
conveyor between a feed station and an outlet or discharge station.
In the embodiment depicted, the conveyor is driven by the drum to
move helically upwardly from the feed station 19 to the discharge
station 20. However, the functions of these stations can be
reversed.
The cage or drum 16 is defined by a central drive shaft 22. upper
and lower spider members 23 and 24 rigidly affixed to said shaft,
and a peripheral wall 25, formed by spaced vertical bars 26 which
frictionally engage the inner edges of belt 17. The upper end of
shaft 22 is journaled in and supported from a heavy duty
radial-thrust bearing 27 (FIG. 4) suitably mounted within the
superstructure, and the lower end of the shaft is journaled in a
radial bearing 28 mounted on the bottom member 12 of the supporting
structure. Where the device is to be employed for refrigeration of
products conveyed on the belt, the lower radial bearing should be
of the self-lubricating type, capable of withstanding cryogenic
temperatures. While the vertical bars 26 are shown as rectangular
in cross-section, bars of circular or other cross-section may be
employed.
The cage or drum is driven by a sprocket 29 mounted approximately
at the upper end of shaft 22, the sprocket being connected through
a driving chain 30 and suitable gearing 31 to a prime mover (FIG.
4). The rigidity and stability of the drum or cage 16 may be
reinforced by supplemental internal supports (not shown).
A belt supporting rack 32 is supported on cantilever support
members 33 circumferentially arranged to extend radially inward
from the uprights 11 at vertically spaced levels. Rack 32 thereby
forms a helical trackway for belt 17 during its travel around drum
16. To reduce friction and wear, the belt rack 32 may be provided
with a low friction surface, such as ultra high molecular weight
polyethylene or the like, to slidably contact the lower surface of
the moving belt. Any form of flat belt may be employed for the
conveyor 17, made up of a plurality of links collapsibly connected
together to permit the belt to bend in an edgewise direction around
the circumferential periphery of the drum. One form of such belt is
disclosed in U.S. Pat. No. 2,872,023. Stainless steel conveyor
belts suitable for this embodiment of the present invention are
commercially available under the Ashworth designations
Omniflex.RTM. and Omni-grid.RTM..
An important feature of the present invention is the novel
arrangement of the means for circulating a heat exchange fluid
across the products carried on the helical conveyor and for
limiting the path of flow of such fluid. As is depicted
particularly in FIGS. 1 and 3 of the drawings, a plurality of axial
flow fans 35, each having a substantially vertical plane of
rotation, are mounted to extend inwardly from the outer uprights
13. While in the specific embodiment illustrated two banks of two
such fans are shown, it will be understood that a larger number of
such fans may be employed, depending among other considerations
upon the number of flights of the conveyor and the extent of heat
exchange required; at least two such fans being needed to carry out
the designed novel push-pull operation in accordance with the
invention. Each pair of fans is arranged to propel the circulated
heat exchange fluid in the path of travel of the conveyor belt and
such that the circulating fluid flows along a portion of the
helical path of the belt from the discharge of the one fan of the
pair to at least a position where the negative pressure of the
suction of the second fan of the pair exists. The circulating gas
stream may be caused to flow concurrently or counter to the
direction of travel of the conveyor. To confine the path of
movement of the circulating heat exchange fluid within a defined
circuit, a scroll case 36 is provided around a major portion of the
periphery of the external edge of the belt. While in the
illustrated embodiment, one pair of cooperating fans is shown at
each level of the fan bank, a larger number of such pairs may be
used at each level, arranged in push-pull relation such that the
heat exchange fluid is propelled along the helical path of the
belt, from the exhaust outlet of one fan to the intake of a
companion fan.
Where the heat exchange system is to be employed for refrigeration
of products carried on the belt, as for example for freezing of
food products, means are provided for the introduction of the heat
exchange fluid into the path of the conveyor movement. As shown in
FIGS. 1 and 3 of the drawings, there is provided at 38 a system for
injection of a cold fluid or refrigerant, such as liquid CO.sub.2
or liquid nitrogen, into the moving fluid stream circulated by the
fans. In the preferred arrangement the liquid refrigerant is
injected at least at each fan location and in a direction such that
the jet of fluid is directed into and counter to the blast of the
fan, thereby effecting rapid vaporization of the refrigerant and in
the case of liquid CO.sub.2 assisting in elimination or reduction
of the build-up of solid CO.sub.2. In addition to the location of
the refrigerant injection points adjacent the fan discharge
stations, any desired number of supplementary injection nozzles
(not shown) may be provided circumferentially spaced at one or more
levels. In the case of CO.sub.2, the refrigerant is advantageously
injected in a direction counter to the direction of bulk flow of
the circulating fluid indicated by arrows 39.
Where the system is to be employed for heating of products carried
on the helical conveyor provision for injection of heat exchange
fluid is not required; instead a heating coil or other heating
means may be provided adjacent the discharge sides of the fans and
along the helical path between the conveyor flights, to heat the
existing circulating air stream.
In instances in which the system is to be employed for
refrigeration of articles carried on the conveyor, the supporting
structure and the rotating cage or drum are enclosed within an
insulated housing 40 comprised of a peripheral wall 41 and top and
bottom closure members 42 and 43, preferably in hermetically sealed
relation. The insulated housing may be formed of spaced metallic
sheets containing therebetween suitable insulating material such as
cellular polyurethane.
An additional feature of the present invention in its preferred
embodiment is the location of the driving means for the cage or
drum outside of the insulated housing, thereby avoiding the
difficulties otherwise encountered in previous refrigeration
installations of this type. Thus, as shown in the illustrated
embodiment, (FIG. 4), the drive shaft 22 is suspended by the heavy
duty radial-thrust bearing 27 which is located external to the cold
environment existing within the insulated enclosure 40, and can be
readily lubricated as needed. No end thrust is imposed on the lower
radial bearing 28, so that a simple self-lubricating bearing can
here be safely employed, capable of withstanding cryogenic or other
extreme temperatures. Moreover, the driving means for the shaft
being located external to the cold environment, such means are not
subjected to the drastic temperature conditions otherwise existing
within the insulated housing, adversely affecting moving mechanical
parts when therein located. Among the important advantages of the
external drive location are:
1. Drive components are not subjected to extreme temperatures;
reducing component cost and increasing life:
(a) Heavily loaded rotating frictional parts requiring efficient
lubrication are located outside the extreme environment where the
most efficient lubricants can be employed. There are no efficient
lubricants for -60.degree. F. or below that are approved by the
U.S.D.A. for incidental food contact. Most lubricants, especially
U.S.D.A. approved, edible lubricants, are adversely affected by
sanitary washdowns.
(b) Drive components are not subjected to sanitation cleaning
procedures and chemicals commonly used in the food industry and can
thus be built of the more commonly used materials such as steel and
aluminum, brass, and the like, rather than stainless steels, epoxy
coatings, or other exotic materials.
(c) Drive components are not subjected to thermal cycling due to
extreme temperature variations commonly experienced by components
designed for the extreme temperature environment and can thus be
designed with closer, more efficient tolerances resulting in longer
life and greater reliability.
2. Drive component maintenance time and cost is reduced;
maintenance personnel do not have to work in the extreme
environment or space limitations necessary with other
arrangements.
To minimize outflow of cold from within housing 40, a low
temperature gas seal may be provided at the place where driving
shaft 22 passes through insulated top 42 of housing 40. Similar
seals may be provided at the places where the upright members pass
through the insulated housing. These low temperature gas seals may
be formed of Teflon or other known low temperature resistant
materials.
By confining the path of flow of the heat exchange fluid in
accordance with the present invention, greater system thermal
efficiencies are attained by reducing gas circulation fan energy.
In thus enabling operation at more desirable operating
temperatures, in the case of systems employing CO.sub.2
refrigerant, the build-up of solid CO.sub.2 otherwise had, is
eliminated or substantially reduced. Because of the push-pull fan
arrangement and the scroll case provision which reduces the
cross-sectional area of the gas flow path, the volume of gas needed
to be circulated to achieve the desired velocity across the product
is markedly decreased and the velocity energy of the gas stream
conserved, thereby affording a higher average gas velocity for
contact of the heat exchange fluid and product.
Moreover, by confining the heat exchange gas circulation to a well
defined circuit, the transfer of heat from the recirculating gas to
potentially solid CO.sub.2 is improved, thereby allowing injection
of the liquid CO.sub.2 refrigerant at the proper gas temperature
point in this circuit, where the gas/solid temperature difference
is high enough to completely sublime the nucleate snow. By locating
a number of refrigerant injection points circumferentially around
the circuit, a low temperature isothermal system is approached
incrementally without sacrificing the temperature differential
required to effect complete sublimation of CO.sub.2 snow. In
addition, by locating the liquid CO.sub.2 injection orifice
directly in the recirculating gas stream and so positioned that the
refrigerant injection blast is against the direction of the
recirculating gas stream, further control over snow sublimation is
achieved, since the nucleate snow particles are thus stripped of
the accompanying cold-gas envelope, exposing them to the warmer
circulating gas stream before they coalesce into larger particles
with lower surface to volume ratios.
The system of the present invention, employing the push-pull fan
arrangement and flow path restricting scroll case, results in
considerable reduction in the volumetric flow rate of the
recirculating gas needed to maintain the desired average velocity,
as compared to previously known spiral gas recirculating systems.
One such known system employs a center cage consisting of a
perforated drum which is pressurized by the gas recirculating fan
or fans and causes the cold gas to blow out radially across the
warm product. In such arrangement the velocity would be directed
into the enclosure walls where it would be lost and solid CO.sub.2
can build up. In a second known arrangement, such as that disclosed
for example in U.S. Pat. No. 3,733,848, the gas flow is confined
only by the enclosure walls, allowing substantial leakage flow
outside the product zone, thereby reducing gas velocity and
permitting solid CO.sub.2 build-up. A comparatively large number of
fans are required to provide the desired average gas flow velocity
across the entire product zone. In using tangential or inline type
linear flow blowers to cover more area in this arrangement, there
is a further increase in required energy by trading the more
efficient propeller-type fan for a less efficient fan.
On the other hand, by the scroll arrangement featured in the
present invention, in addition to the attained reduction in
volumetric gas flow rate necessary to maintain the desired average
velocity, the gas is essentially confined within the product zone,
such that in systems employing liquid CO.sub.2 refrigerant any
solid CO.sub.2 that may be formed is confined to such product zone
where it can sublime. By incorporating two fan banks in a series of
push-pull arrangement within a properly designed scroll casing, the
angular momentum induced helps direct the gas velocity around the
product zone to the suction of the opposite fan bank as contrasted
to previous arrangements.
Moreover, the arrangement of the fans in accordance with the
invention whereby the heat exchange fluid is projected essentially
directly into the path of the products travelling on the conveyor,
the spurting of such heat exchange fluid at comparatively high
velocity through the ports at the product inlet and discharge
stations is avoided. The low velocity leak of a small portion of
the heat exchange fluid at these ports in the system of the
invention, however, is sufficient to establish a counterflow
barrier against significant influx of external air into the area
enclosed by the insulated housing.
As is common in installations of the type described employing
CO.sub.2 refrigerant, provision is made to prevent undesired
leakage of the CO.sub.2 into the atmosphere at the product inlet
and outlet of the heat exchange system. Thus, exhaust ducts (not
shown) may be provided adjacent to product inlet 19 and outlet 20
to draw off the CO.sub.2 there leaking out, these ducts being
connected to a venting conduit provided with an exhaust blower.
While in the preferred embodiment illustrated and above described,
the drum or cage is disclosed as made up of a plurality of spaced
vertical bars 26, in some instances if desired, the circumferential
wall of the drum or cage may be solid or a solid curtain may be
attached to the inside or outside faces of these bars. Such solid
wall formation is not recommended for systems designed for handling
of food products and the like in which sanitation needs to be
considered.
* * * * *